This invention relates to the hydrogenolysis of hydrobenzoins [1,2-bis(aryl)ethane-1,2-diols]. It represents an efficient and highly selective way of removing the 1,2-diol functionality from hydrobenzoins. More particularly, this invention relates to the hydrogenolysis of hydrobenzoins in the presence of a catalyst comprising cobalt carbonyl to yield 1,2-bis(aryl)ethanes in which the hydrobenzoin 1,2-diol functionality has been removed efficiently and selectively.
Hydrogenolysis of benzylic alcohols to hydrocarbons under mild conditions with heterogeneous catalysts, particularly palladium on charcoal, is well known in the art. See, for example, Baltzly et al, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 65, 1984 (1943). Thus benzyl alcohol is readily amenable to hydrogenolysis by most common hydrogenolysis catalysts. However, when such commonly employed catalysts are routinely applied to hydrobenzoins, they suffer from several disadvantages, the most obvious of which is their failure in many instances to induce the desired hydrogenolysis. For example, 4,4'-dihydroxyhydrobenzoin fails to react when subjected to hydrogenolysis under conditions similar to those employed by Baltzly et al. Similarly, although good selectivity for the hydrogenolysis of hydrobenzoin to 1,2-diphenylethane (bibenzyl) using platinum on carbon (charcoal) and alcoholic palladium chloride as the catalyst has been described in Zelinsky et al, Chemische Berichte, 66, 872 (1933), the extension of the catalyst to other hydrobenzoins, for example, 4,4'-dihydroxyhydrobenzoin is nevertheless unsuccessful.
Furthermore, such commonly employed hydrogenolysis catalysts are not easily recycled for reuse in subsequent hydrogenolysis reactions. As a result, the routine use of such catalysts for large technical scale processes is prohibitively wasteful and expensive.
Hydrogenolysis of benzylic alcohols to hydrocarbons with homogeneous catalysts, for example, dicobalt octacarbonyl and/or cobalt hydrocarbonyl has also been described. See, for example, Wender et al, Journal of the American Chemical Society, 73, 2656 (1951). The selectivity for production of toluene from benzyl alcohol, however, was reported to be only 63 percent, with 32 percent selectivity for the homologation product, 2-phenylethanol.
It is therefore an object of the present invention to overcome the above disadvantages and therefore provide an improved and more economically and commercially feasible hydrogenolysis process in which a mixture of hydrogen and carbon monoxide is employed with a homogeneous catalyst comprising cobalt carbonyl to hydrogenolyze hydrobenzoins to form 1,2-bis(aryl)ethanes.
Another object of the present invention is to provide a more selective and reactive hydrogenolysis system for the removal of the 1,2-diol functionality from hydrobenzoins, while simultaneously facilitating product isolation and catalyst recovery and recycle for reuse in subsequent reactions without substantial catalyst decomposition and loss.
Still another object of the present invention is to provide a hydrogenolysis process enabling the efficient and selective production of 1,2-bis(4-hydroxyphenyl)ethane from 4,4'-dihyroxyhydrobenzoin.
These and other objects will become apparent to those skilled in the art from the accompanying description of the invention.